Antioxidant supplements tended to increase cancer survival rates, shrink tumors and did not interfere with chemotherapy treatments, according to a new review.

Researchers from the Institute for Integrative Cancer Research and Education in Evanston, Illinois, reviewed 19 randomized, clinically-controlled trials involving 1,554 participants, most of whom had advanced or relapsed cancer. Seven of the trials used glutathione, four trials used melatonin, two trials used vitamin A, two trials used an antioxidant mixture that included beta-carotene and selenium, and four additional trials used, individually, N-acetylcysteine (NAC), vitamin C, vitamin E or ellagic acid, an antioxidant in fruits and nuts such as cranberries and walnuts.

Scientists concluded that chemotherapy treatments were at least as effective in participants who took antioxidant supplements as in those who took placebo, and that the antioxidant group had similar or better survival rates than did the placebo group. In 18 out of the 19 trials, tumors shrank and responded as well or better for those who took antioxidants compared to those who took placebo. In 15 out of 17 trials that analyzed the toxic effects of the chemotherapy, such as diarrhea, weight loss, nerve damage and low blood counts, the antioxidant group had similar or lower toxicity rates compared to placebo.

There has been a long-running debate in the medical community about whether or not antioxidant supplements alter the effect of cancer chemotherapy. One theory is that because chemotherapy works by creating oxidants, antioxidants may diminish this effect. Another theory is that antioxidants reduce the toxic effects of chemotherapy. The study authors noted that by reducing side effects from chemotherapy, antioxidant supplements may permit people to continue cancer chemotherapy treatment without stopping, interrupting or reducing dosing, which may improve cancer health outcomes.

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